feat(routing): land on Journal at root; move Knowledge to /knowledge

Routing changes:
- / now redirects to /journal (Journal becomes the home view)
- /knowledge becomes a real route pointing at KnowledgeView (was a redirect to /)
- /notes redirect target updated from / to /knowledge (the Knowledge surface,
  which is where the notes-related dashboard lives)

To revert (Knowledge as home): change the redirect target on the / route
back to "/knowledge". Knowledge stays a real route either way, so the swap
is a one-line edit.

Nav: Knowledge link in AppHeader now points to /knowledge. The "active" check
simplified to route.path === "/knowledge" since / is no longer Knowledge's
home. The brand logo link stays at "/" — clicks still go "home", which is
now Journal.

Keyboard shortcuts in App.vue (Escape, g h, g t) still navigate to "/" and
correctly land on Journal via the redirect — no change needed there.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/router/index.ts

@@ -5,13 +5,16 @@ const router = createRouter({
   history: createWebHistory(),
   routes: [
     {
+      // Root lands on the journal. To revert to Knowledge as home, change
+      // the redirect target below to "/knowledge" (Knowledge stays a real
+      // route at /knowledge, so the swap is a one-line edit).
       path: "/",
-      name: "knowledge",
-      component: () => import("@/views/KnowledgeView.vue"),
+      redirect: "/journal",
     },
     {
       path: "/knowledge",
-      redirect: "/",
+      name: "knowledge",
+      component: () => import("@/views/KnowledgeView.vue"),
     },
     {
       path: "/login",
@@ -45,7 +48,7 @@ const router = createRouter({
     },
     {
       path: "/notes",
-      redirect: "/",
+      redirect: "/knowledge",
     },
     {
       path: "/notes/new",